1. Field of the Invention
The present invention relates to an insulative ceramic compact for use in, for example, a multilayer circuit board. Specifically, the present invention relates to an insulative ceramic compact that can be advantageously used in a composite multilayer circuit board on which a semiconductor device or a variety of electronic parts is mounted, and can be obtained by firing in conjunction with a conductive material such as copper or silver.
2. Description of the Related Art
Recent tendencies to accelerate and to use electronic equipment in higher frequencies keep on expanding. With such tendencies, demands for the accelerating, higher-density mounting and higher-density packing of electronic parts which are used in such electronic equipment are increasing. To satisfy these demands, multilayer circuit boards are conventionally used as substrates on which semiconductor devices and various electronic parts are mounted. In such a multilayer circuit board, the substrate houses a conductive circuit and an electronic part functional device to thereby further miniaturize electronic equipment.
Alumina has been conventionally frequently used as a material for constituting the multilayer circuit board. Alumina has a relatively high firing temperature from 1500xc2x0 C. to 1600xc2x0 C., and high-melting (refractory) metals such as Mo, Moxe2x80x94Mn and W must be generally used as materials for conductive circuits housed in such a multilayer circuit board composed of alumina. However, these refractory metals have a high electric resistance.
Strong demands have been therefore made on the use of a metal such as copper as a conductive material, which metal has a lower electric resistance and is available at a lower cost than the refractory metals. To use copper as a conductive material, the use of a glass ceramic or crystallized glass which can be obtained by firing at low temperatures of 1000xc2x0 C. or less has been proposed (e.g., Japanese Unexamined Patent Application Publication No. 5-238774).
Alternatively, the use of a ceramic having a thermal expansion coefficient close to that of Si as a material for such multilayer circuit boards has been proposed, in consideration of connection with semiconductor devices such as Si chips (Japanese Unexamined Patent Application Publication No. 8-34668).
However, these conventional substrate materials that can be fired at low temperatures have low mechanical strengths and a low Q value, and the type and proportion of the deposited crystal phase are readily affected by the firing process.
Additionally, the substrate materials described in Japanese Unexamined Patent Application Publications No. 5-238774 and No. 8-34668 cannot be significantly sintered in conjunction with highly dielectric materials having a high thermal expansion coefficient.
Accordingly, an object of the present invention is to provide an insulative ceramic compact that can solve the above problems, can be obtained by firing at low temperatures and can be obtained by firing in conjunction with a conductive material having a relatively low melting point such as silver or copper, has a low relative dielectric constant, and has satisfactory high-frequency characteristics and a high thermal expansion coefficient.
Another object of the present invention is to provide a multilayer ceramic substrate which is composed of the aforementioned insulative ceramic compact, can be obtained by firing at low temperatures, has a low relative dielectric constant and satisfactory high-frequency characteristics, and can be obtained by sintering in conjunction with a highly dielectric material having a high thermal expansion coefficient, as well as to provide a ceramic electronic part using the multilayer ceramic substrate.
Specifically, the present invention provides, in an aspect, an insulative ceramic compact which includes a fired mixture of (A) a MgAl2O4 ceramic powder; and (B) a glass powder including from about 13 to 50% by weight of silicon oxide calculated as SiO2, from about 8 to 60% by weight of boron oxide calculated as B2O3, from 0 to about 20% by weight of aluminum oxide calculated as Al2O3, and from about 10 to 55% by weight of magnesium oxide calculated as MgO.
The content of silicon oxide in terms of SiO2 in the glass powder is from about 13 to 50% by weight, and preferably from about 20 to 30% by weight relative to the total weight of the glass powder. If the content of silicon oxide is less than about 13% by weight, the resulting sintered compact has a decreased degree of crystallization and a decreased Q value. In contrast, if it exceeds about 50% by weight, the resulting glass has an excessively high melting temperature.
The content of boron oxide in terms of B2O3 in the glass powder is from about 8 to 60% by weight and preferably from about 30 to 60% by weight, relative to the total weight of the glass powder. The boron oxide mainly acts as a fusing agent (flux). If the content of boron oxide in terms of B2O3 is less than about 8% by weight, the melting temperature becomes excessively high, and if it exceeds 60% by weight, the resulting sintered compact has a decreased moisture resistance.
In the glass powder, the content of aluminum oxide in terms of Al2O3 is from 0 to about 20% by weight relative to the total weight of the glass powder. The aluminum oxide content in terms of Al2O3 may be 0% by weight, that is, aluminum oxide may not be necessarily contained in the glass powder. Accordingly, when the insulative ceramic compact according to the present invention contains no aluminum oxide, it is an insulative ceramic compact composed of a fired mixture of (A) MgOxe2x80x94MgAl2O4 ceramic powder and (B) a glass powder including from about 13 to 50% by weight of silicon oxide in terms of SiO2 and from about 3 to 60% by weight of boron oxide in terms of B2O3.
When the content of aluminum oxide in terms of Al2O3 in the glass powder exceeds about 20% by weight, the resulting sintered compact cannot become sufficiently dense and has a decreased Q value. The lower limit of the aluminum oxide content in terms of Al2O3, if it is contained, is any value more than 0% by weight.
The glass powder preferably contains from about 10 to 55% by weight of MgO. MgO plays a role to decrease a melting temperature in the manufacture of glass and also plays a role as a component constituting crystals in a crystallized glass. Particularly, a MgOxe2x80x94B2O3 compound exhibits a Qf value of several ten thousands gigahertz or more and is a predominant factor to exhibit satisfactory high-frequency characteristics. If the content of MgO is less than about 10% by weight, the resulting insulative ceramic compact has a decreased Q value, and if it exceeds about 55% by weight, the insulative ceramic compact may have excess amounts of deposited crystals to thereby deteriorate the strengths of the substrate.
The glass powder for use in the present invention preferably further includes at least one alkaline earth metal oxide selected from among BaO, SrO and CaO in a proportion of about 20% by weight or less relative to the total weight of the glass powder.
The alkaline earth metal oxide serves to decrease the melting temperature in the manufacture of glass and to increase the thermal expansion coefficient of glass. If the content of the alkaline earth metal oxide exceeds about 20% by weight, the resulting insulative ceramic compact may have a decreased Q value.
The glass powder for use in the present invention preferably further includes at least one alkali metal oxide selected from among Li2O, K2O and Na2O in a proportion of about 10% by weight or less, and more preferably from about 2 to 5% by weight, relative to the total weight of the glass powder. The alkali metal oxide serves to decrease the melting temperature in the manufacture of glass. If the content of alkali metal oxide exceeds about 10% by weight, the resulting insulative ceramic compact may have a decreased Q value.
The invented insulative ceramic compact preferably further includes zinc oxide in a proportion calculated as ZnO of about 15% by weight or less, more preferably about 10% by weight or less, relative to the total weight of the ceramic compact. The zinc oxide serves to decrease the firing temperature. However, if the content of zinc oxide in terms of ZnO exceeds about 15% by weight, the resulting sintered compact may not become sufficiently dense in some cases.
The zinc oxide is preferably contained as a component other than the ceramic powder and glass powder, but may be contained as a component constituting the glass component.
The invented insulative ceramic compact preferably further includes copper oxide in a proportion in terms of CuO of about 3% by weight or less, and more preferably about 2% by weight or less, relative to the total weight of the ceramic compact. The copper oxide serves to decrease the firing temperature. However, if the content of the copper oxide exceeds about 3% by weight, the resulting insulative ceramic compact may have a decreased Q value. The copper oxide is preferably contained as a component other than the ceramic powder and glass powder, but may be contained as a component constituting the glass component.
In the invented insulative ceramic compact, the weight ratio of the ceramic powder to the glass powder is preferably from about 20:80 to 80:20 and more preferably from about 30:70 to 50:50. If the ratio of the ceramic powder is higher than the above range, the resulting sintered compact may have a decreased density. If the proportion of the glass powder is higher than the above range, the sintered compact may have a decreased Q value.
The invented insulative ceramic compact may preferably have a Q value of about 700 or more as determined at a frequency of 15 GHz. If the insulative ceramic compact has a Q value of about 700 or more, it can be used as a circuit device substrate recently used in the high-frequency range.
A glass powder obtained by calcining a glass composition at a temperature from about 700xc2x0 C. to 1400xc2x0 C. may be used as the glass powder.
In another aspect, the present invention provides a multilayer ceramic substrate which includes an insulative ceramic layer composed of the insulative ceramic compact according to the present invention; and plural inner electrodes formed in the insulative ceramic layer.
In the multilayer ceramic substrate, a second ceramic layer may be laminated at least on one side of the insulative ceramic layer, which second ceramic layer has a dielectric constant higher than that of the insulative ceramic layer.
The plural inner electrodes in the multilayer ceramic substrate may be arrayed in parallel with each other with the interposition of at least part of the insulative ceramic layer to thereby constitute a capacitor.
The plural inner electrodes may include conductive coils constituting an inductor.
In addition and advantageously, the present invention provides a ceramic electronic part including the invented multilayer ceramic substrate and at least one electronic part device, which electronic part device is mounted on the multilayer ceramic substrate and constitutes a circuit with the plural inner electrodes.
The ceramic electronic part may further include a cap being fixed to the multilayer ceramic substrate so as to surround the electronic part device. The cap is preferably a conductive cap.
The ceramic electronic part according to the present invention may further include plural outer electrodes formed only on the underside of the multilayer ceramic substrate, and plural conductive through-holes that are electrically connected to the outer electrodes and are electrically connected to the inner electrode or electronic part device.
The present invention also relates to a multilayer ceramic electronic part which includes a ceramic sintered compact composed of the invented insulative ceramic compact, plural inner electrodes that are arrayed inside the ceramic sintered compact, and plural outer electrodes that are formed on the outer surface of ceramic sintered compact and are electrically connected to any of the inner electrodes.
In the aforementioned multilayer ceramic electronic part, the plural inner electrodes may be arrayed in parallel with each other with the interposition of the ceramic layer to thereby constitute a capacitor unit. In the multilayer ceramic electronic part, the plural inner electrodes may further include plural conductive coils in addition to the inner electrodes constituting the capacitor unit, which plural conductive coils are connected with each other to thereby constitute a multilayer inductor unit.
Furthermore, another object of the present invention is to provide an insulative ceramic compact that can solve the above problems, can be obtained by firing at low temperatures and can be obtained by firing in conjunction with a conductive material having a relatively low-melting such as silver or copper, has a high Q value in the high-frequency range and a low relative dielectric constant, and has satisfactory high-frequency characteristics and a high thermal expansion coefficient.
Another object of the present invention is to provide a multilayer ceramic substrate which is composed of the aforementioned insulative ceramic compact, has a low relative dielectric constant and a high Q value and therefore has satisfactory high-frequency characteristics, has a high thermal expansion coefficient and can be obtained by sintering in conjunction with a highly dielectric material, as well as to provide a ceramic electronic part using the multilayer ceramic substrate.
Specifically, the present invention provides, in an aspect, an insulative ceramic compact being composed of a fired mixture of (A) at least one selected from among a Mg3B2O6 ceramic powder and a Mg2B2O5 ceramic powder; and (B) a glass powder including from about 13 to 50% by weight of silicon oxide in terms of SiO2, from about 8 to 60% by weight of boron oxide in terms of B2O3, from 0 to about 20% by weight of aluminum oxide in terms of Al2O3, and from about 10 to 55% by weight of magnesium oxide in terms of MgO.
In the present invention, at least one of a Mg3B2O6 ceramic powder and a Mg2B2O5 ceramic powder is used as ceramic powder (A). Specifically, a Mg3B2O6 ceramic powder alone or a Mg2B2O5 ceramic powder alone may be used, and a mixture of these powders may also be used.
The content of SiO2, B2O3, Al2O3, etc., in the glass powder is as described above for the reasons stated earlier.
In the invented insulative ceramic compact, the weight ratio of the ceramic powder to the glass powder is preferably from about 20:80 to 80:20 and more preferably from 40:60 to 60:40. If the ratio of the ceramic powder is higher than the above range, the resulting sintered compact may have a decreased density. If the proportion of the glass powder is higher than the above range, the sintered compact may have a decreased Q value.
In particular, the invented insulative ceramic compact can be obtained by firing a mixture containing the ceramic powder and the glass powder at low temperatures of 1000xc2x0 C. or less, and can be obtained by firing in conjunction with a low-melting metal such as copper or silver. Accordingly, the invented insulative ceramic compact can be advantageously used, for example, in a multilayer ceramic substrate using a conductive material composed of such a low-melting metal.
The invented insulative ceramic compact may preferably have a Q value of about 700 or more as determined at a frequency of 15 GHz. If the insulative ceramic compact has a Q value of about 700 or more, it can be used as a recent circuit element substrate for use in the high-frequency range.
The invented insulative ceramic compact has a high thermal expansion coefficient, and can be sintered in conjunction with a highly dielectric material having a high thermal expansion coefficient to thereby easily and stably yield an integrally sintered compact composed of the invented insulative ceramic compact and a highly dielectric ceramic.
In another aspect, the present invention provides a multilayer ceramic substrate including an insulative ceramic layer composed of the insulative ceramic compact; and plural inner electrodes formed in the insulative ceramic layer.
In the multilayer ceramic substrate, a second ceramic layer may be laminated at least on one side of the insulative ceramic layer, which second ceramic layer has a dielectric constant higher than that of the insulative ceramic layer.
The plural inner electrodes in the multilayer ceramic substrate may be arrayed in parallel with each other with the interposition of at least part of the insulative ceramic layer to thereby constitute a capacitor. The plural inner electrodes may include conductive coils constituting an inductor.
In addition and advantageously, the present invention provides a ceramic electronic part including the aforementioned multilayer ceramic compact and at least one electronic part device, which electronic part device is mounted on the multilayer ceramic substrate and constitutes a circuit with the plural inner electrodes.
The ceramic electronic part may further include a cap being affixed to the multilayer ceramic substrate so as to surround the electronic part device. The cap is preferably an electrically conductive cap.
The electronic part according to the present invention may further include plural outer electrodes formed on the underside alone of the multilayer ceramic substrate, and plural conductive through-holes that are electrically connected to the inner electrode or electronic part device.
The present invention also relates to a multilayer ceramic electronic part which includes a ceramic sintered compact composed of the invented insulative ceramic compact, plural inner electrodes that are arrayed inside the ceramic sintered compact, and plural outer electrodes that are formed on the outer surface of ceramic sintered compact and are electrically connected to any of the inner electrodes.
In the aforementioned multilayer ceramic electronic part, the plural inner electrodes may be arrayed in parallel with each other with the interposition of a ceramic layer to thereby constitute a capacitor unit.
In the multilayer ceramic electronic part, the plural inner electrodes may further include plural conductive coils in addition to the inner electrodes constituting the capacitor unit, and the plural conductive coils are connected with each other to thereby constitute a multilayer inductor unit.